The impact ionization generation rate in the narrow gap semiconductors InSb and InAs is calculated by a Monte Carlo procedure. The impact ionizing collision is treated as an additional scattering mechanism in calculating the transport parameters. Electron–electron scattering is included directly in addition to ionized impurity and polar optical phonon scattering. The results are compared with experimental data obtained for InSb and InAs of carrier concentrations in the range 1014 to 1016 cm−3. Agreement between theory and experiment is good with discrepancies being interpreted in terms of exact band non‐parabolicities and further carrier–carrier interactions.

The electron transport properties of the narrow‐gap semiconductors InSb and InAs are calculated by a Monte Carlo procedure. The drift velocity and electron distribution function are found to be affected at high electric fields by the inclusion of impact ionization collisions, and the negative differential conductivity is correspondingly reduced.

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falo Alto, CA PIN DIODES have been used for several years to accomplish switching in the VHF spectrum. Due to their relatively high minimum series resistance ( "0.5 ohm), they cannot be used in the UHF spectrum for band switching in applications requiring high circuit Q. A low resistance UHF (< 0.2 Q a t 20 mA, reverse bias capacitance, Cj G.8 pF) switching PIN diodc has been developed for this purpose, using techniques ba5ed on optimizing the diode performance and an improved device technology.An optimization technique was developed to minimize the resistance of the device from geometric considerations. The optimization program was devised by breaking the PIN diodc resistance into two parts: current-independent resistance and current-dependent resistance. The current-independent rcsistance (P' diffusion, N+ substrate, metal-semiconductor contacts) is PC Ppt PN+ pNt R =-+-where, A is the active area of the diode, pr is the contact resistivity, pp+ and pNt are the average resistivity of the P+ and Nt regions, respect&ely, and QP+ and . ! -? , t arc the lengths of the P 'and N+ regions, respectively.The current-dependent resistance can be written using the standard charge control model where, w is the width of the I layer, is the average elcctron and hole mobility, I is the diode current, and rcff is the effective minority carrier lifetime. Since Teff is a function of the I-layer width w and the current density J, this relation must he included.The exact relation is relatively complex, but the following empirical formula is a good approximation:where, 7 , is the effective lifetime at a given I-layer width, wo, and a given current density, J,. Using this relationship and the standard capacitance equationwhere, E is the dielectric constant, and C. is the junction capacitance, the currcnt-dependent part (I-layer resistance) can be written as J The mobility used is corrected due to carrier-carrier interactions at high current densities. Since the mobility is a slowly varying function of current density, it can be easily calculated by itcration. Typically two or three iteratious are adcquatc.The total resistance of the diode is thc sum of equations (I) and (5), There is obviously a minimum in the rcsistance as a function o f area, A. The area corresponding to minimum resistance is A . mm =&)6Using this area the I-layer width is determined from equation (4). This completely defines the active region of the diode.The total diode resistance can be reduced by decreasing K1 and K2. Several processing steps can be varied to decrease K1. rhin and heavily doped P+ diffusions are used to reduce the resistance of the Pf diffusion. By the use of Ti metal contacts and by keeping the surface concentration on both the Pf diffusion and theN+ substrate high (>lozo ~r n -~) :the metal contact resistivities are reduced.To reduce the N' substrate resistance, a process was developed to obtain a thin ( 3 p m ) substrate. The SEM photograph in Figure 1 shows the structure of the diode with the thin substrate.This device w a~ processed on (I ...

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